1. Field of the Invention
This invention relates to the use of a plasma or a glow discharge for dissociating one or more gases into reactive and non-reactive ionic and reactive and non-reactive neutral species, and in particular, to concentrating such a plasma.
2. Description of the Prior Art
Plasma apparatus can be divided into two broad categories, downstream or remote plasma and direct plasma. In downstream plasma, the article(s) are not immersed in the glow discharge, as it is in direct plasma. The result is a purely chemical and multi-directional process resulting in a somewhat more gentle treatment of the article(s) because high power electromagnetic waves at high frequency are not coupled through the article(s) and there is no heating from direct ion bombardment. In either type of apparatus, it is known in the art to employ some type of plasma for processing one or more article(s).
Typically, one or more reactive gases (such as air, oxygen-based gases, or halogen-based gases, including fluorine, chlorine, bromine, or other equivalent gases, as well as gas molecular compounds having one or more oxygen or halogen atoms), are used in combination with other gases, due to the highly reactive nature of the reactive gas(es) in a plasma chamber.
In the prior art, in downstream (remote) plasma processing, the problems encountered regarding the article can include: high energy photons reaching the surface of the article, electrical charges reaching the surface of the article, or a decrease in the concentration of reactive neutrals caused by diffusion of reactants throughout the entire volume of the vacuum chamber. For example, the prior art tries to remove the photons with passageways between the plasma exhaust of the plasma source and the article, where the passageway has an elbow (a bend of 90 degrees) or baffles (which increase the distance between the source and the article in a convoluted manner) to prevent photons from reaching the article. And the prior art also attempts to remove the electrical charges by means of recombining electrical charges in plasma, depending on the distance between the exhaust of the plasma source and the surface of the article.
However, the prior art relies on the plasma parameters (i.e., dissociating power and pressure) of the plasma source in order to extend the plasma. But once the maximum power available and minimum operating pressure are reached, the prior art falls short in concentrating a plasma for treating articles downstream. In view of the foregoing, what is needed is an improved method and apparatus to efficiently and selectively concentrate a plasma to direct it at an article.